A “long hour” refers to the “decimal hour”, equal to 2.4 hours, exactly one tenth of a day, sometimes called a “deciday”. The decimal hour was an official unit of French Decimal Time, during the French Revolution, during the 1790s. Since then there are periodic attepts to revive it. It sometimes features in scifi to represent a futuristic or alternate system of measurement.

The chief said to be there in three hours, but did she mean the old hours or the new long hours?

Long hour is 2 and a half hours that the administration thinks is necessary to throw 35 kids in a packed classroom and make them wait while everyone else eats lunch. 27 minutes of lunch 2 hours of hell.

Secretary: we have too many kids to just section them off into 4 groups. We’ll have to go with 5 half hour long lunches.
Principal: well lets just see what happens.